XXXV International Symposium on Multiparticle Dynamics 2005 Rick Field University of Florida (for the CDF & D0 Collaborations) KROMĚŘÍŽ, CZECH REPUBLIC August 9-15, 2005 CDF Run 2 ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Jet Physics and the Underlying Event at the Tevatron Outline of Talk The Jet Cross Section in Run 2 at the Tevatron: MidPoint Algorithm (CDF/D0) and KT Algorithm (CDF). The b-Jet Inclusive Cross Section in Run 2 at the Tevatron (CDF/D0). High PT “jets” probe short distances! KT Algorithm The b-bbar Jet Cross Section and Correlations (CDF). Jet-Jet Correlations (D0). Understanding and Modeling the “Underlying Event” in Run 2 at CDF. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The TeVatron delivered more than 350 pb-1 in 2004! 1 fb-1 milestone! ~1.1 fb-1 delivered Proton-antiproton collisions s = 1.96 TeV (Run 1 = 1.8 TeV) 36 bunches: 396 ns crossing time Peak luminosity ~ 1032 cm-2 s-1 12-20 pb-1 per week! More than six times Run 1! CDF has ~900 pb-1 on tape! The TeVatron delivered more than 350 pb-1 in 2004! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Next-to-leading order parton level calculation Jets at 1.96 TeV “Theory Jets” “Real Jets” Next-to-leading order parton level calculation 0, 1, 2, or 3 partons! Experimental Jets: The study of “real” jets requires a “jet algorithm” and the different algorithms correspond to different observables and give different results! Experimental Jets: The study of “real” jets requires a good understanding of the calorimeter response! Experimental Jets: To compare with NLO parton level (and measure structure functions) requires a good understanding of the “underlying event”! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Rick Field - Florida/CDF Jet Corrections Calorimeter Jets: We measure “jets” at the “hadron level” in the calorimeter. We certainly want to correct the “jets” for the detector resolution and effieciency. Also, we must correct the “jets” for “pile-up”. Must correct what we measure back to the true “particle level” jets! Particle Level Jets: Do we want to make further model dependent corrections? Do we want to try and subtract the “underlying event” from the “particle level” jets. This cannot really be done, but if you trust the Monte-Carlo models modeling of the “underlying event” you can try and do it by using the Monte-Carlo models (use PYTHIA Tune A). Parton Level Jets: Do we want to use our data to try and extrapolate back to the parton level? This also cannot really be done, but again if you trust the Monte-Carlo models you can try and do it by using the Monte-Carlo models. The “underlying event” consists of hard initial & final-state radiation plus the “beam-beam remnants” and possible multiple parton interactions. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Dø Inclusive Jet Cross Section MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5) L = 380 pb-1 Two rapidity bins Highest PT jet is 630 GeV/c Compared with NLO QCD (JetRad, Rsep = 1.3?) Log-Log Scale! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Dø Di-Jet Cross Section MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5) L = 143 pb-1 |yjet| < 0.5 Compared with NLO QCD (JetRad, Rsep = 1.3) Update expected this Winter ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

CDF Inclusive Jet Cross Section MidPoint Cone Algorithm (R = 0.7, fmerge = 0.75) Data corrected to the parton level L = 385 pb-1 0.1 < |yjet| < 0.7 Compared with NLO QCD (JetRad, Rsep = 1.3) ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

CDF Inclusive Jet Cross Section Run 1 showed a possible excess at large jet ET (see below). This resulted in new PDF’s with more gluons at large x. The Run 2 data are consistent with the new structure functions (CTEQ6.1M). Run I CDF Inclusive Jet Data (Statistical Errors Only) JetClu RCONE=0.7 0.1<||<0.7 R=F=ET /2 RSEP=1.3 CTEQ4M PDFs CTEQ4HJ PDFs ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Rick Field - Florida/CDF KT Algorithm kT Algorithm: Cluster together calorimeter towers by their kT proximity. Infrared and collinear safe at all orders of pQCD. No splitting and merging. No ad hoc Rsep parameter necessary to compare with parton level. Every parton, particle, or tower is assigned to a “jet”. No biases from seed towers. Favored algorithm in e+e- annihilations! Will the KT algorithm be effective in the collider environment where there is an “underlying event”? KT Algorithm Raw Jet ET = 533 GeV Raw Jet ET = 618 GeV CDF Run 2 Only towers with ET > 0.5 GeV are shown ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

KT Jet Cross-Section NLO parton level theory corrected to the “particle level”! Data at the “particle level”! Correction factors applied to NLO theory! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

KT Jet Cross-Section NLO parton level theory corrected to the “particle level”! Data at the “particle level”! 7 7 8 Correction factors applied to NLO theory! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The b-Jet Inclusive Cross-Section See the talk later this week by Mario Campanelli on “Heavy Flavor States at CDF”! Inclusive b-Jet Cross Section The data are compared with PYTHIA (tune A)! Data/PYA ~ 1.4 Comparison with MC@NLO coming soon! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Dø m-Tagged Jets Correlations MidPoint Cone Algorithm (R = 0.5) Require muon in R = 0.5. L = 300 pb-1 |yjet| < 0.5 PT(m) > 5 GeV/c m-Tagged Jets Cross Section D0 Jets containing heavy flavor often contain muons (e.g. b→c +W→ m+n). Searching for muons in jets enhances the heavy flavor content. Data/PYTHIA flat ~ 1.3. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The b-bbar DiJet Cross-Section ET(b-jet#1) > 30 GeV, ET(b-jet#2) > 20 GeV, |h(b-jets)| < 1.2. Systematic Uncertainty Preliminary CDF Results: sbb = 34.5  1.8  10.5 nb QCD Monte-Carlo Predictions: PYTHIA Tune A CTEQ5L 38.71 ± 0.62nb HERWIG CTEQ5L 21.53 ± 0.66nb MC@NLO 28.49 ± 0.58nb Differential Cross Section as a function of the b-bbar DiJet invariant mass! Predominately Flavor creation! Large Systematic Uncertainty: Jet Energy Scale (~20%). b-tagging Efficiency (~8%) ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The b-bbar DiJet Cross-Section ET(b-jet#1) > 30 GeV, ET(b-jet#2) > 20 GeV, |h(b-jets)| < 1.2. Preliminary CDF Results: sbb = 34.5  1.8  10.5 nb QCD Monte-Carlo Predictions: PYTHIA Tune A CTEQ5L 38.7 ± 0.6 nb HERWIG CTEQ5L 21.5 ± 0.7 nb MC@NLO 28.5 ± 0.6 nb MC@NLO + JIMMY 35.7 ± 2.0 nb Differential Cross Section as a function of the b-bbar DiJet invariant mass! JIMMY Runs with HERWIG and adds multiple parton interactions! Proton AntiProton “Flavor Creation” b-quark Underlying Event Initial - State Radiation Final State Radiation JIMMY: MPI J. M. Butterworth J. R. Forshaw M. H. Seymour Adding multiple parton interactions (i.e. JIMMY) to enhance the “underlying event” increases the b-bbar jet cross section! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

b-bbar DiJet Correlations Tune A! Differential Cross Section as a function of Df of the two b-jets! The two b-jets are predominately “back-to-back” (i.e. “flavor creation”)! Pythia Tune A agrees fairly well with the Df correlation! Not an accident! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Dø Jet-Jet Correlations Jet#1-Jet#2 Df Distribution MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5) L = 150 pb-1 (Phys. Rev. Lett. 94 221801 (2005)) Data/NLO agreement good. Data/HERWIG agreement good. Data/PYTHIA agreement good provided PARP(67) = 1.0→4.0 (i.e. like Tune A). ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The “Underlying Event” in Run 2 at CDF The “underlying event” consists of hard initial & final-state radiation plus the “beam-beam remnants” and possible multiple parton interactions. “Transverse” region is very sensitive to the “underlying event”! New CDF Run 2 results (L = 385 pb-1) : Two Classes of Events: “Leading Jet” and “Back-to-Back”. Two “Transverse” regions: “transMAX”, “transMIN”, “transDIF”. Data corrected to the particle level: unlike our previous CDF Run 2 “underlying event” analysis which used JetClu to define “jets” and compared uncorrected data with the QCD Monte-Carlo models after detector simulation, this analysis uses the MidPoint jet algorithm and corrects the observables to the particle level. The corrected observables are then compared with the QCD Monde-Carlo models at the particle level. For the 1st time we study the energy density in the “transverse” region. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The “Transverse” Regions as defined by the Leading Jet Charged Particles (pT > 0.5 GeV/c, |h| < 1) Calorimeter Towers (ET > 0.1 GeV, |h| < 1) Look at the charged particle density in the “transverse” region! “Transverse” region is very sensitive to the “underlying event”! Look at charged particle and calorimeter tower correlations in the azimuthal angle Df relative to the leading calorimeter jet (MidPoint, R = 0.7, fmerge = 0.75, |h| < 2). Define |Df| < 60o as “Toward”, 60o < -Df < 120o and 60o < Df < 120o as “Transverse 1” and “Transverse 2”, and |Df| > 120o as “Away”. Each of the two “transverse” regions have area DhDf = 2x60o = 4p/6. The overall “transverse” region is the sum of the two transverse regions (DhDf = 2x120o = 4p/3). ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Charged Particle Density Df Dependence Refer to this as a “Leading Jet” event Subset Refer to this as a “Back-to-Back” event Look at the “transverse” region as defined by the leading jet (|h| < 2) or by the leading two jets (|h| < 2). “Back-to-Back” events are selected to have at least two jets with Jet#1 and Jet#2 nearly “back-to-back” (Df12 > 150o) with almost equal transverse momenta (PT(jet#2)/PT(jet#1) > 0.8) and PT(jet#3) < 15 GeV/c. Shows the Df dependence of the charged particle density, dNchg/dhdf, for charged particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for 30 < ET(jet#1) < 70 GeV for “Leading Jet” and “Back-to-Back” events. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

Tuned PYTHIA 6.206 PYTHIA 6.206 CTEQ5L CDF Default! PYTHIA 6.206 CTEQ5L Parameter Tune B Tune A MSTP(81) 1 MSTP(82) 4 PARP(82) 1.9 GeV 2.0 GeV PARP(83) 0.5 PARP(84) 0.4 PARP(85) 1.0 0.9 PARP(86) 0.95 PARP(89) 1.8 TeV PARP(90) 0.25 PARP(67) 4.0 Run 1 Analysis Plot shows the “Transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, Set B (PARP(67)=1) and Set A (PARP(67)=4)). Old PYTHIA default (more initial-state radiation) Old PYTHIA default (more initial-state radiation) New PYTHIA default (less initial-state radiation) New PYTHIA default (less initial-state radiation) ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransDIF” PTsum Density PYTHIA Tune A vs HERWIG “Leading Jet” “Back-to-Back” “transDIF” is very sensitive to the “hard scattering” component of the “underlying event”! Use the leading jet to define the MAX and MIN “transverse” regions on an event-by-event basis with MAX (MIN) having the largest (smallest) charged PTsum density. Shows the “transDIF” = MAX-MIN charge PTsum density, dPTsum/dhdf, for pT > 0.5 GeV/c, |h| < 1 versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransMAX/MIN” PTsum Density PYTHIA Tune A vs HERWIG “Leading Jet” “Back-to-Back” Shows the charged PTsum density, dPTsum/dhdf, in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG (without MPI) at the particle level. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransMAX/MIN” ETsum Density PYTHIA Tune A vs HERWIG “Leading Jet” “Back-to-Back” Shows the ETsum density, dETsum/dhdf, in the “transMAX” and “transMIN” region (all particles |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG (without MPI) at the particle level. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransDIF” ETsum Density PYTHIA Tune A vs HERWIG “Leading Jet” “Back-to-Back” “transDIF” is very sensitive to the “hard scattering” component of the “underlying event”! Use the leading jet to define the MAX and MIN “transverse” regions on an event-by-event basis with MAX (MIN) having the largest (smallest) charged PTsum density. Shows the “transDIF” = MAX-MIN ETsum density, dETsum/dhdf, for all particles (|h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransMAX/MIN” ETsum Density PYTHIA Tune A vs JIMMY JIMMY was tuned to fit the energy density in the “transverse” region for “leading jet” events! JIMMY: MPI J. M. Butterworth J. R. Forshaw M. H. Seymour “Leading Jet” “Back-to-Back” Shows the ETsum density, dETsum/dhdf, in the “transMAX” and “transMIN” region (all particles |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. Compares the (corrected) data with PYTHIA Tune A (with MPI) and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c) at the particle level. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransMAX/MIN” PTsum Density PYTHIA Tune A vs JIMMY “Leading Jet” “Back-to-Back” Shows the charged PTsum density, dETsum/dhdf, in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. Compares the (corrected) data with PYTHIA Tune A (with MPI) and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c) at the particle level. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransMAX/MIN” Nchg Density PYTHIA Tune A vs JIMMY “Leading Jet” “Back-to-Back” Shows the charged particle density, dNchg/dhdf, in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. Compares the (corrected) data with PYTHIA Tune A (with MPI) and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c) at the particle level. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“TransMAX/MIN” <PT> PYTHIA Tune A vs JIMMY “Leading Jet” “Back-to-Back” Shows the charged particle <PT> in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c) at the particle level. ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

“Underlying event” important in jet (and b-jet) production! Summary The MidPoint jet cross section at the Tevatron is consistent with theory (CTEQ61M) over 9 decades! KT Algorithm The KT algorithm works fine at the Tevatron and theory/data (CTEQ61M) look flat! The measured the inclusive b-jet section, b-bbar jet cross section and correlations, are behaving as expected from theory - nothing goofy! CDF Run 2 Proton AntiProton “Flavor Creation” b-quark Underlying Event Initial - State Radiation Final State Radiation “Underlying event” important in jet (and b-jet) production! We are making good progress in understanding and modeling the “underlying event”. We have PYTHIA Tune A and JIMMY tune A, however, we do not yet have a perfect fit to all the features of the “underlying event”. We are working on new improved Run 2 tunes! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The Future Some CDF-QCD Group Analyses! Much more QCD physics to come from the Tevatron! Some CDF-QCD Group Analyses! Jet Cross Sections and Correlations: MidPoint and KT algorithms with L = 1 fb-1! DiJet Mass Distributions: Df distribution, compositness. Heavy Flavor Jets: b-jet and b-bbar jet cross sections and correlations. Z and W Bosons plus Jets: including b-jets. Jets Fragmentation: jet shapes, momentum distributions, two-particle correlations. Underlying Event Studies: distributions as well as averages for charged particles and energy for jet, jet+jet, g+jet, Z+jet, and Drell-Yan. Pile-Up Studies: modeling of pile-up. Monte-Carlo Tuning: New Run 2 PYTHIA tune, tuned JIMMY, PYTHIA 6.3, Sherpa, etc.. Analyses using 1fb-1 of data by Winter 2006! ISMD 2005 August 11, 2005 Rick Field - Florida/CDF

The Past CDF (2005) Feynman, Field, & Fox (1978) 30 GeV/c! Predict large “jet” cross-section 30 GeV/c! Feynman quote from FFF: “At the time of this writing, there is still no sharp quantitative test of QCD. An important test will come in connection with the phenomena of high PT discussed here.” ISMD 2005 August 11, 2005 Rick Field - Florida/CDF